Peter. Speaking as someone who's favourite site is metres away from a landfill, causing the site to stink and get strewn with litter when the wind takes its fancy I have to say that I totally disagree with your notion that do nothing is the worst option.
Doing nothing will not destroy any more archaeology for the sake of development. The current issues with traffic noise dust etc. may be a concern to you now, but is not the threat of further loss of archaeology far more of a concern?
Stonehenge, as with Thornborough is filled with people looking to provide a "quick fix" to the problem. both of these are a direct result of development pressure and in no way are based on the thought of what is right for the monument.
Unless something is actually damaging the site, doing nothing cannot be seen as the worst option IMHO.